Moisture-heat exchangers of the aforesaid kind are known to the art. One such moisture-heat exchanger is disclosed in U.S. Pat. No. 5,109,471. This known moisture-heat exchanger is comprised of two passive moisture-heat exchanger elements and an intermediate air humidifying and heating arrangement. Moistening of the inhalation air is achieved with water that is introduced into water passageways such as to wet a perforated paperboard plate which covers the end surface on the inside of one moisture-heat exchanger element. The water is heated in the moisture-heat exchanger with the aid of resistors that function to heat heat-transfer means which include a perforated plate and which are mounted between the two passive moisture-heat exchanger elements.
The air humidifying means of the known apparatus presents considerable resistance to the flow of air through the moisture-heat exchanger and therewith reduces the rate of air flow and also the throughflow of inhalation and exhalation air. This resistance to air flow is mainly caused by the fact that the perforated plates cover large parts of the through-flow area.
Because of the construction of the heating means of the known SUBSTITUTE SHEET (RULE 26) apparatus, the air that flows through the heating means is heated only partially and, furthermore, unevenly. Because the heating means is located in a region between two passive moisture-heat exchange elements, the moisture-heat exchanger has a large axial extension.
DE-A 4 126 028 teaches a moisture-heat exchanger apparatus which includes a moisture-heat exchanger element that accommodates a plurality of pipes through which water is delivered to said element and therewith moisten the same. This known apparatus also includes a heating means which comprises an annular heating element which is spaced from the moisture-heat exchanger element both radially and axially. The greatest drawback with this apparatus is that water is delivered to only a few discrete regions within the moisture-heat exchanger element, resulting in uneven moistening of the inhalation air.
WO91/19527 teaches a moisture-heat exchanger apparatus which includes a moisture-heat exchanger element in the form of a plate, and an inhalation-air heating resistor spaced from the plate. The apparatus also includes a pipe whose outlet orifice is located adjacent the surface of the resistor and which delivers water thereto. The greatest drawbacks with this apparatus are mainly that moistening of the air is ineffective because water is delivered to the resistor, which also creates the risk of short-circuiting, and because heating of the air is incomplete when the resistor has the form of a rod, or the through-passage of air is impaired when the resistor has the form of a grid or grating.
SE-C 501 042 teaches a moisture-heat exchanger in which a band-like or wire-like heating element is mounted between layers therein that are positioned parallel with the direction of flow of the inhalation air. Manufacture of this apparatus is complicated and the apparatus presents a relatively high resistance to air flow. An air humidifying means in the form of a diffusion rod lies against one end of the moisture-heat exchanger and delivers moisture thereto. However, delivery of moisture to the moisture-heat exchanger is uneven and often incomplete, therewith rendering the apparatus less effective.